The present invention relates to a hydraulic device comprising a valve housing with a movable valve body arranged inside the valve housing, at least a hydraulic chamber provided inside said valve housing, and at least a control mechanism for the control of said movable valve body, wherein the valve housing comprises a plurality of combined elements, at least two of said elements being co-axially arranged so relative to each other that an annular space is formed between said two parts, the valve body is substantially sleeve-shaped and arranged inside said annular space in the valve housing, and said valve body is provided with a plurality of apertures to make a flow of hydraulic liquid possible in the radial direction through the valve body.
In many known applications, there is a need to perform a quick percussion motion and/or to perform a controlled motion, while heavy forces shall be transmitted, wherein some kind of a hydraulic device often is preferred (where hydraulic force transmission is utilised. According to prior art, such hydraulic devices are controlled/adjusted by a servo-valve suitable for large flows of oil at high pressures, which implies that the valve is very expensive. Further, it forms a unit of its own at a distance from the hydraulic device. Often, it may be the question of servo-valves with large outer dimensions, which thus are very bulky and may have a weight of hundreds of kilos. Further, a hydraulic hose must often be used between the servo valve and the hydraulic device, which as such implies an increased risk for damage. The high pressures, large flows of oil and the compressibility of the hydraulic hoses also imply that it will be difficult to meet high demands on rapidity and accuracy. Moreover, such servo-valves require a comparatively long adjustment time, often up to 100 msec, which is not satisfactory in many applications.
An application where long adjustment times are unsatisfactory is percussion presses. Percussion presses are previously known through e.g. U.S. Pat. No. 3,965,799, U.S. Pat. No. 4,028,995, and U.S. Pat. No. 4,635,531, which show arrangements with quick adjustments but where the hydraulic piston is part of the valve function. As a consequence, the function of the hydraulic piston may not be controlled at will, but the function is connected to the position of the hydraulic valve inside the valve housing. As to the field of applications, said devices are therefore limited to oscillating machines, in the first hand hammers, which move quickly between two positions, entirely without any possibility of control therebetween.
Said known type of percussion presses is not suitable for forming using high kinetic energy, which is a type of material treatment, such as cutting and punching, forming of metal components, powder compaction, and similar operations, at which the initial percussion is crucial, and as the speed of the press piston may be-about 100 times higher or more than in conventional presses. This fact puts very high requirements on the valve arrangement, as it must be possible to perform extremely quick adjustments of large flows, while high pressures exist in the hydraulic system in order to be able to adequately develop high forces. The operation principle is based on the generation of short-term but very high kinetic energy. It is not unusual that the power at the acceleration of the striking piston amounts to at least 20-30 KN in an average-sized percussion press. In order to be able to market such a machine, it is necessary to be able to offer a rugged construction, and at the same time it is desirable to be able to offer a valve assembly which is less expensive and which requires less space.
A condition for achieving such a valve function is the provision of a sleeve-shaped valve body between two co-axial portions of the valve housing, which thus forms an annular space, in which the sleeve-shaped valve body is provided. Said basic principle is indeed previously known through U.S. 4,559,863, but said publication refers to a stamp hammer where the hydraulics arein principle used only to lift the hammer. The only pressure which drives the hammer downwards is a residual pressure, which is accumulated in a low pressure accumulator after a quick return. In such a device, the gravity, and not the hydraulics, performs the essential operation in connection with the percussion. Thus, such a construction is not suitable at forming utilising high kinetic energy, wherein extremely high accelerations are necessary. Another disadvantage of the known device is that it does not make quick adjustments possible. Furthermore, it does s not make it possible to control the function of the hydraulic piston independent of the position of the hydraulic piston. Further, the known device is not balanced with reference to forces acting in the radial direction, which would inexorably lead to problems, if extremely high hydraulic pressures are applied.
It is realised that the application illustrated above is only one of many fields of application, where there is scope for essential improvements regarding the valve assembly and its mode of operation. Thus, it is evident that many of the problems which have been identified in connection with the percussion presses are also found within many other operation fields where it is as important to try to find a solution of the problems, or at least some of the identified problems. An example of such another field is hydraulic adjusting means, which, according to the above described servo-valve assembly, is today often an expensive and/or a too bulky solution, and/or a too slowworking device.
The object of the invention is to eliminate or at least to minimise the above mentioned problems, which is achieved by a hydraulic device according to the above description, which is characterised in that the valve body is located inside the valve housing in such a way that it is essentially, preferably entirely, balanced with reference to the hydraulic forces acting in the radial direction, that said valve body in the vicinity of said apertures is provided with edge portions at both the inner and outer surfaces of the valve body, which edge portions interact with edge portions and channels located inside the valve housing, so that hydraulic liquid is allowed to flow from each one of said channels and beyond and between each of said edge portions, when the valve body is positioned inside the valve housing to allow a flow of liquid to and from said hydraulic chamber, and that said edge portions at a second position of the valve body interacts in a sealing manner, so that the hydraulic liquid cannot flow to or from said hydraulic chamber.
Thanks to the solution according to the invention, very short flow passages are obtained, which makes extremely quick processes possible. Further, according to the invention it is also possible to control the hydraulic piston independent of the position of the hydraulic piston. In this connection, it is an advantage that the valve body is formed as a sleeve-shaped means, as large flow apertures thereby may be achieved with comparatively small motions.
It is realised, thanks to the invention, that a solution with all the advantages which are obtained may be used in a lot of different applications.
According to further potential aspects of the invention:
the edge portion of the valve body is an integrated part of at least one of said apertures;
the valve body is essentially symmetrically shaped with reference to a plane running centrally across the valve body;
the maximum, necessary movement of the valve body within the valve housing to move the valve body from a shut to an open position is between 0.1 and 3% of the outer diameter of the sleeve, preferably below 2%, and more preferred below 1%.
the movement of the valve body between the shut and open positions is at least substantially performed in the axial direction with reference to the hydraulic piston;
the adjustment time for the valve body from one end position to the other end position is below 10 msec, preferably below 5 msec;
the hydraulic piston is provided with at least two annular, force-transmitting surfaces, which are opposite each other, wherein preferably the upper annular surface is larger than the other one;
the hydraulic piston comprises three co-axial, integrated units with different outer diameters, wherein the centre portion is provided with the largest diameter;
at least one control mechanism is activated in a hydraulic manner;
the control mechanism comprises means provided to be capable to move the valve body, which means are movable in apertures in the valve housing, wherein the apertures essentially correspond to the shape of said means, and that said apertures communicate with an annular channel intended to be pressurised by hydraulic oil;
the means have a circular, outer jacket surface, and that said apertures consist of circular holes extending in the axial direction;
the control mechanism is activated in a magnetic manner;
the control mechanism comprises at least one ferro-magnetic portion provided at the valve body and at least one electromagnet provided at the valve housing;
the electromagnet is cooled by hydraulic oil;
the valve housing is provided with a pressure connection and a tank connection in one or several of its side walls;
the device is a part of a percussion/pressing means intended to perform quick percussions and to transmit heavy forces, wherein the valve body has a minimum diameter between 3 and 500 mm, preferably exceeding 50 mm, and more preferred exceeding 80 mm;
at least one of said edge portions is provided with symmetrically arranged recesses, which, at a small movement of the valve body from its shutting position, allows a minor flow to occur in the radial direction through the valve body;
the length of the edge portions and hence the total area of the apertures may vary by varying the position of the valve body in the rotating direction;
the valve body is positioned by the hydraulic pressure acting on the annular surfaces, wherein the hydraulic fluid to at least one of said surfaces is controlled by a valve slide provided in the valve body and working according to known principles for copying valves, so that the surrounding valve body slavishly follows said valve slide, which in turn is positioned by a double-acting electromagnet;
a hydraulic piston provided in the hydraulic chamber with at least one outwardly facing end surface, wherein the hydraulic piston is located inside the valve housing in a co-axial manner;
the valve housing is provided with two separate hydraulic chambers.